Process of producing oxygen



May 15, 1,951 F. J. JENNY ET'AL 2,552,559

PROCESS OF PRODUCING OXYGEN Filed Dec. 5, 1945 iatented May 1:5, i951 UNITED STATES PATENT OFFICE PROCESS F PRODUCING OXYGEN Frank J. Jenny, New York, N. Y., and Edward G.

Scheibel, Nutley, N. Jr, as signors to Hydrocarbon Research, Inc., New York, N. Y.

Application December 5, 1945, Serial No.- 632,860 9 Claims. (o1. a2-175.5)

This invention relates to the production of oxygen by the liquefaction and rectification of air, and more particularly to an economical method of obtaining oxygen in high purity and in high yield without the use of chemical reagents to effect the removal of carbon dioxide and moisture present in air.

All temperatures herein are in degrees F. and pressures in pounds per square inch gauge'.

Oxygen is commonly produced by partial liquefaction of airV and rectification at low temperatures ;4 preferably rectification is conducted 'in two stages at different pressures. The refrigeration necessary for liquefaction isV supplied to the air after it has been compressed and Water-cooled to approximately room temperature, by indirect heat exchange with the eiuent products of rectification. However, an additional amount of refrigeration must be supplied to compensate for cold losses resulting from the difference in enthalpy between the incoming air and the outgoing products of rectiiication and for heat leaks into the system. Methods of supplying this refrigeration heretofore used, involve compressing at least a portion of the incoming air to pressures as high as 3000 pounds and expanding with or without the performance of Work to produce a temperature drop;` or compressing all the incoming air to about 600 pounds and after the air has been partially cooled by the products of rectification expanding a portion of the air. These methods are wasteful from the standpoint of compressor energy and require a great deal of equipment in the form of extra compressorsintercoolers and expanders.

For economical operation it is essential to recover the cold content of the outgoing products of rectication. This is usually accomplished by passing theseproducts in heat transfer relationship with the incoming air. In older systems'in order to avoid deposition of frost and solid carbon dioxide in the tubular countercurrent heat exchangers through which the air is passed in indirect heat exchange relation with the outgoing products of rectication, theair is treated in driers and caustic scrubbers to removewater and carbon dioxide prior to admittance of the air into the heat exchangers. Even With this treatment the exchangers had to be thawed out regularly to remo-ve the frost (which term is used in a generic sense to include both snow and ice) which caused stoppingup of the apparatus.

Morerecently it has been suggestedto usecold accumulators or regenerators (hereinafterl referred to as heat exchangers) of large cold abv sorbing capacity through which the Warm incoming air and the cold products of rectication are alternately passed with periodically reversed operation so that streams of warm air are flowed through the same packing-filled spaces that the cold separated oxygen and nitrogen traversed during the previous step in the process, the highboiling impurities deposited in these spaces during the passage of air therethrough being removed by sublimation during the subsequentl flow in a reverse direction of the products of rectication. The use of these reversing heat exchangers in a process in which the air is compressed to re1- atively high pressure results in more costly operation from the standpoint of horsepower requirements because upon every reversal, which may take place every three minutes, the volume of compressed air in the heat exchangers is 10st and must be again replaced. Moreover, in the operation of such reversing heat exchangers it is important not tolet the temperature at the exit end of the exchangers drop to a point where a part of the air becomes liquid because this liquid adheres to the surface ofthe exchangers and is wasted upon reversal of ilow. On the other hand the temperature conditions under which the exchangers are operated should be such as to obtain complete purging of the carbon dioxide' deposited therein upon reversal of flow which usuallyrequires having the air exit end of at least one of the exchangers at a low temperature, i. e., at or near the'dew point of air.

It is an object of the present invention to provide a process for producing oxygen by the liquefaction andrectiiication of air in which moisture and carbon dioxide are moved from the air Without the use of chemical reagents and which involves the use of reversing heat" exchangers through which flow in heat exchange relation the outgoing products of rectication and theincoming air, the process being operated atrelatively low pressures of the order ofabout '70 pounds to about pounds gauge so thatthe loss of compressed air inthe exchangers upon each' reversal is small andl inY which the reversing exchangers are operated so that moisture and carbon dioxide are completely removed fromthe air during their flow therethrough during one step' of the process and upon reversal the frost and carbon dioxide deposited in the exchangers during the preceding step are completelyV removed andgthis without liquefactionof air taking place inthe exchangers. Another object of the invention is to provide a process for producing oxygen of high purity from air with greatly reduced equipment and power costs as compared with ex-Y isting procedures. Other objects and advantagesY of this invention will be apparent from the following detailed description.

In accordance with this invention a stream of each other throughV two of which pass respectively streams of oxygen and nitrogen products of rectification in heat exchange relation with the air passing through a third path. One of Vthe streams flowing between the rst zone and a second zone is refrigerated by expanding a minor portion of the total air introduced into the process, say from 5% to 10%, preferably about 7%, to produce refrigeration which is imparted either to the remainder of the air, prior to its ii'ow through 'the' second zone or to the rectiiication products, prior to their flow through the first zone, thus introducing into the process an amount o cold adequate to compensate for cold losses resultingV from the difference in enthalpy between the air introduced into and the products of rectication withdrawn from the process and for heat leaks into the system. The temperature conditions in the first zone or exchanger are such that substantially all moisture present in the air is removed therefrom in the form of frost. The temperature conditions in the second or subsequent exchanger are such as to effect substantialy complete removal of carbon dioxide from the air in its passage therethrough.

at the colder end of the second exchanger where the oxygen and nitrogen products of rectiiication enter and air leaves the exchanger, there is maintained between these products of rectification and the countercurrent stream of air a temperature difference in the range of about 5 to about 10 F., preferably about 6 to about 8Q F. This temperature difference Vis the diierence between the temperature of the air and the weighted average temperature of the products of rectication, all temperatures being taken at the colder -end of the second exchanger. For the purposes of VthisV invention, the weighted average temperature of the products of rectication is calculated by multiplying the temperature of the oxygen product stream by the volume percentage of the stream based on the combined volume of the products of rectication and adding thereto the corresponding figure obtained by multiply ing the temperature of the nitrogen product stream by its volume percentage. Thus, for example, if the rectification system is operated to produce two streams of substantially pure oxygen and pure nitrogen, the weighted average temperature of the two streams would be approximately the sum of of the oxygen Vstream temperature and 80% of the nitrogen stream temperature. Periodically the flow of air and nitrogen through their respective paths in the two exchangers is reversed so that upon reversal the air ows through the paths in the two exchangers through which during the preceding stepV the nitrogen had passed and the nitrogen hows through the paths in the two exchangers through which had previously passed the air. The nitrogen removes, by sublimation, the carbon dioxide deposited during the preceding step in the second exchanger and the frost deposited during the preceding step in the rst exchanger.

Operating in this manner complete purging of carbon dioxide isobtained upon each reversal of now. Likewise complete purging of frost is obtained so that the equipment may be operated continuously. v Y 1 Since the refrigeration necessary to compensate for cold losses resulting from the difference in enthalpy between the incoming air and the outgoing products of rectification and for heat leaks into the system is supplied by expanding relatively low-pressure air, it can be supplied economically, i. e., with low power cost. Furthermore, the expansion is carried out at a temperature of the order of about 80.F. so that no liquefaction occurs in the expander and, accordingly, the expander operates at high efficiency.

The apparatus required for the practice of the process is more economical and simpler than that required for prior known processes in that the heat exchanger surface is reduced to a mini-V mum and the need forv caustic scrubbers, driers and compressors for high pressure air is eliminated. Recoveries as high as about 93% of the oxygen of the total air introduced into the process Y may be obtained when operating in accordance with this invention by expanding not more than 7% of the total air introduced into the system and passing the expanded air in indirect heat exchange relation with the reminder of the air supplied to the second exchanger or with the nitrogen or oxygen productsV of rectiiication which are then passed in heat exchange relation with the incoming air in the iirst exchanger, or by directly mixing the expanded air with the "effluent nitrogen product of rectification and passing the resultant mixture in heat exchange relation with the incoming air in the first exchanger. The last-mentioned procedure vis preferred.

In the preferred embodiment illustratedin the drawing, the single figure of which illustrates diagrammatically a preferred layout of apparatus for practicing the process of this invention, the equipment shown for the practice of the process involves a, pair of heat exchangers having therebetween an expansion engine or turbine to expand a portion of the air and the present Vdescription will be conned to the present illustrated embodiment of the invention. It will be understood, however, that the process may be carried out in other equipment, for example, each of the two exchangers in series may be replaced by two or more smaller exchangersplaced in series and/or parallel, if desired, although this is objectionable from the standpoint of increasing construction costs, or the number of heat ex change paths in each exchanger may be increased over the B-path construction shown'in the drawing. Hence, the scope of the invention is not confined to the embodiment herein described.

In theV drawing reference character i0 indicates a heat exchanger which may be oi any wellknown type. In the embodiment shown in the drawings it consists of a single shell in which are provided three paths, namely, interior zone H through which ilows in one and the same direc tion throughout the operation of the exchanger the oxygen product of rectification. Paths i2 and i3 are provided within the shell of the exchanger through which periodically flow air and the nitrogen product of rectication in heat exchange relation with each other and with the oxygen. The heat exchanger has in each of the paths suitable ns of heat-conducting material, e. g., copper, promoting rapid and ecient heat exchange between the gaseous media flowing therethrough. As the construction of the heat exchanger per se does not form part of this invention and as it may be of any well-known type, it is believed further description thereof is unnecessary.

The ow of the air and nitrogen through their respective paths is periodically reversed so that during one step of the process air flows through path I2 and nitrogen through path I3, and upon reversal, during the succeeding step air ows through path I3 and nitrogen through path I2.

Reversal of now is accomplished by suitably positioning the compound reversing valves lli and I5 which may be of any well-known type. Valve I4 is disposed in the pipe line system consisting of air inlet pipe I6 leading into valve lil, and pipe lines I'I and i8 leading from the valve to paths I2 and I3, respectively. At the base of the` heat exchanger It lines I9 and 2i? are positioned leading from paths I2 and I3, respectively, to the valve I5.

A` second heat exchanger 2| is provided in the form of a shell having therein paths 22, 23 and 2li provided with iins to promote heat exchange as in the case of the exchanger It. Path is the path through which the oxygen product of rectification flows from the rectication system hereinafter described to a pipe line 25 which communicates with path II of heat exchanger IEB. The base portions of paths 22 and 23 of heat exchanger 2I communicate with pipe lines 33 and 27, respectively, which are communicably connected with a compound valve 23 which may be of the same type as valves I4 and I5. At the upper portions paths 22 and 23 communicate respectively with lines 23 and 30 which in turn communicate with a compound reversing valve 3i which may be of the same type as the other reversing valves.

Reversing exchangers I and 2l may be placed in vertical, horizontal or any other desired position. Likewise, when these exchangers are ar-A ranged vertically, the colder end may be above or below the warmer end.

Compressed air flows from valve I to an exfpansion engine or turbine 32, which may be of any conventional type, through line 33, branch line 33a and valve 33h. By controlling valve 33h, the air owing through line 33 is divided into two streams, one stream representing about 7% of the compressed air passing through the expander 32 and then flowing through line 9a into the nitrogen stream line 3. The remaining 93% of the air continues to flow through line 33 which communicates with compound valve 23.

With the arrangement of valves and piping shown ow of nitrogen and air through heat exchangers I0 and 2l may be periodically reversed, say every three minutes, so that during an initial period of operation air flows through path l2, through line I9, valve I5, line 33, valve 28, line 2P, path 22 in heat exchanger 2l into the pipe line 23, valve 3| and thence to line 34 leading to the non-reversing heat exchanger 35 which communicates with the rectification system hereinafter described. At the same time, nitrogen flows through pipe line 36 leading from the non-revers ing heat exchanger 35 into valve 3l, line 30, through path 23 in heat exchanger 2|, through line 2'I, valve 28, line 0, valve I5, pipe line 2li, path I3 in heat exchanger I0, leaving this path through pipe line I8 and passing through valve i4 to the atmosphere or other suitable disposal point. Upon reversal (as shown by dotted arrows and valve settings), the air flows through valve 14,1111?. la, path es, pipeline zo, valve I5. line 33, valve 28, pipe line 2'I, and thence through the path 23, leaving this path through pipe line and passing through valve 3l and pipe line into the non-reversing exchanger 35. Atlthe same time, the nitrogen iiows from heat exchange er 35 through pipe line 33 into valve 3|, thence 'through pipe line 29, path 22 in heat exchanger 2l, pipe line 23, valve 28, line 9i, valve I5, line I3 into path I2, thence through line I'I into valve lfl and thence to the atmosphere or other suitable disposal point.

The rectification system comprises a two-stage rectification column 3'I, the lower section 38 of which is operated at a pressure of about 72 pounds gauge and the upper section 39 of which is operated at pressures of from about 4 pounds to about 10 pounds gauge, preferably at about 5 pounds gauge. This column as is customary is provided with rectification plates of the bubblecap or other desired type. The lower section 38 of the column 3'I communicates with a condenser and has a liquid collecting shelf 4I disposed immediately below the condenser 40 for collecting liquid nitrogen. Pipe line 42 leads from this shelf 4I to a non-reversing heat exchanger 43 which in turn communicates through a pressure reducing valve d4 with the top portion of the upper section 39 as indicated by the reference character 45. Condenser 40 acts as a reboiler for the upper section 39 of the column 3T.

From the base portion of the lower section 38 a pipe line 43 for the flow of crude oxygen (containing approximately 40% oxygen) passes to a non-reversing heat exchanger 41 which communicates through pipe line 43 having a pressure reducing valve 43 therein with the low-pressure section 39 at an intermediate point indicated by the reference character 50. A line 5I having a pressure reducing valve 52 therein, leads from condenser 40 to a nitrogen line 53 leading to the non-reversing heat exchanger 35. A line 54 leads from the top of low-pressure column 39 to the heat exchanger 43, the nitrogen flowing through this line passing through the heat exchanger 43 then through line 55 and heat exchanger 4l into line 56 which communicates with line 53. An oxygen line 51 leads from the lower part of the low-pressure section 30 of column 3l to zone 24 of heat exchanger 2I. The heat exchangers 35, 43 and 41 and the two-stage fractionating column 3`I may be of any conventional type.

Two separate fractionating columns, suitably interconnected, may be used in place of the twostage column 31 shown. It will be understood that the equipment throughout is heat insulated to minimize loss of cold.

For a desirable operating range, air at a pressure of 70 pounds to 85 pounds gauge and a temperature of 70 to 110 F. is introduced into heat exchanger I0, leaving this exchanger at a temperature of to 100 F. and substantially the same pressure.

About 5% to about 10% by volume of this cold air stream is expanded to provided suicient refrigeration to decrease the temperature of the nitrogen stream passing from exchanger 2l to exchanger l0 by 5 to 15 F. The products of rectication leave the heat exchanger l0 at a temperature of 60 to 100 F. The remainder of the cold air stream enters heat exchanger 2l at a temperature of 75 to 100 F. and leaves at a temperature of 260 to 280 F. The nitrogen enters heat exchanger 2| at a temperature 75 of 265 to 285 F. and leaves at a temperature 'l lof 80 to 105 F. The oxygen enters heat exchanger 2| at a temperature of 288 to 293 F. and leaves at a temperature of 80 to 105 F.V The several streams suffer only a small pressure drop in flowing through the two reversring exchangers in series.

One example of the operation of the process of :this invention is described below; it will be understood this example is given for purposes of exfemplirlcation only and the invention is not lim- Iited thereto. Y

Air under pressure of about 75 pounds gauge fand temperature of about 100 F. is supplied through line l5, valve I4 and line l1 to heat exchanger l iiowing through cooling path-I2 in which it is cooled to a temperature of 80 F. Of theair flowing from valve l5, 7% by volume is expanded in engine 32, the pressure of the expanded air being about pounds and its temperature 215 F.; this cold expanded air discharges into line 9 conveying nitrogen at a temperature of 83.l. F. from exchanger 2l -to exchanger |0 and on mixing with the nitrogen lowers the temperature to 92.1 F., the remainder of the air at a temperature of 80 F. passes through the cooling path 22 in the heat exchanger 2i leaving this path at a temperature of 273 F. Substantially all moisture is removed in the form of frost in path i2 of heat exchanger I8 and all carbon dioxide is removed in solidied form in cooling path 22 of heat exchanger 2I. The air then flows through the heat exchanger 35 in heat exchange relation with ni- I' trogen and enters high-pressure column 38 at a temperature of 275 F. and a pressure of 72 pounds. y

Crude oxygen at a temperature oi' 278 F. and pressure of 72 pounds leaves the base of Ycolumn 38, flows through the heat exchanger 41 where its temperature is reduced to 286 F. and upon iiow through the pressure reducing valve 89 is flashed, entering column 39 at a temperature of 310 to 315 F. and a pressure of 5 pounds. Pure oxygen is withdrawn through line 57 at a temperature ci 2927 F. and a pressure of 5 pounds and flows through path 24, its teinperaturel being increased to 83.1 the oxygen at this temperature flowing through path Il of heat exchanger i9 and being withdrawn from Vthis path at a temperature of 90 F. and at a pressure of i pound. l

Nitrogen at a temperature of about 286 F. and a pressure of 72 pounds is withdrawn through line 5l and passes through valve 52 its temperature being reduced to a temperature of about 815 as a result of the expansionV through the pressure reducing valve 52. Nitrogen at a temperature of 315 F. and a pressure of 5 pounds is withdrawn through line 54 and ows through heat exchanger 43 where its temperature is raised to about 304 F. The nitrogen flows from heat exchanger 03 through heat exchanger lll and mixes with that from line 5I; the nitrogen stream thus produced at a temperature of 294 F. iows through line 53 into and, 'through heat exchanger 35 Where the temperaand the oxygen streams have a weighted average temperature of nearly 281 F. while at this point the airis at a. temperature of 273 F. A temperature difference of about 8 F. is therefore maintained. It will be noted that at the point where the air enters and the oxygen and nitrogen leave the heat exchanger 2l the difference in temperature is approximately 3 F., the air being at a temperature oi F. and the oxygen and nitrogen at 83.1 F. Y

From the heat exchanger 2i nitrogen flows through line 21, reversing valve 28, line 9 where it mixes with the expanded air at a temperature Yof 215 F., the temperature of the nitrogen stream being thereby decreased to 92.1 F. at which temperature it enters valve I5 andrflows through line 20 into and through path l'3 inheat exchanger I0, leaving this exchanger at a temperature of F. and a pressure slightly above atmospheric, say 1 pound gauge.

Upon reversal (as shown by dotted arrows and valve settings), which may take place every three minutes, the air flows through the cooling paths I3 and 23, respectively, of heat exchangers I8 and 2| and nitrogen flows through paths i2 and 22, respectively, of heat exchangers i8 and 2i. The low is otherwise substantialiy the same and the temperature and pressure conditions remain the same. The nitrogen in its ow through path 22 of heat exchanger 2l removes by sublimation the carbon dioxide deposited in this path by the air during the preceding step. Likewise, the nitrogen in its flow through path l2 of heat exchanger l0 removes from this path the frost deposited therein from the 'pair during the preceding step. Thus in the continued operation upon each reversal the nitrogen effects removal of the carbon dioxide and frost deposited in lthe paths through Which the air had passed during the preceding step of the process. Y

'It will be noted that this invention provides a process for producing oxygen of high purity without the use of chemical reagents which process may be operated continuously for long periods of time without shut-downs for the purpose of removing solid carbon dioxide or frost, which process is economical to operate particularly in that the refrigeration which must be supplied to compensate for cold losses resulting from the difference in enthalpy between incoming air and the outgoing products of rectification and for heat leaks into the system is supplied at a point in the process where the temperatures are relatively high so that it can be supplied eiciently and economically.

The expression reversal is used herein in the sense commonly employed in this art, namely, to mean the switching of the W of the air and the nitrogen streams, so that upon each reversal the air ows through the path through which had previously flowed the nitrogen, and the nitrogen flows through the path through which had previously flowed the air.

Since certain changes may be made in carrying out the above process without departing from the scope of the invention it is intended that all matter contained Vin the above description shall be interpreted as illustrative and not in a limiting sense. Y

What is claimed is:

1. A process for producing oxygen by the llquefaction and rectication of air, which comprises, passing streams of oxygen and nitrogen series, each of saidV zones containing at least three paths in heat exchange relation with each other, passing a stream of air at about 70 to about 85 pounds gauge through a third path in the first zone in heat exchange relation with the oxygen and nitrogen streams flowing through their' respective paths in said first Zone, expanding a minor portion of the air leaving said first zone and imparting the refrigeration thus produced to at least one of said oxygen and nitrogen streams flowing through said first zone, passing the remainder of the air through a third path in the second zone-in heat exchange relation with the oxygen and nitrogen streams owing through their respective paths in said second zone, regulating the iiow of air, nitrogen and oxygen into and from said second zone so that the temperature within said second zone is such as to eect substantie y complete removal of carbon dioxide from the air in its passage through its path in said second zone and the difference between the temperature of the air and the weighted average temperature of the nitrogen and oxygen at the colder end of said second zone :falls within the range of about to about 10 F., and periodically reversing the flow of air and nitrogen through their respective paths in said zones, the air upon reversal flowing through the paths through which had previously flowed the nitrogen and the nitrogen flowing through the paths through which had previously ilowed the air, whereby upon each reversal the nitrogen substantially completely rremoves the carbon dioxide deposited in said second zone during the preceding step of the process.

2. A process for producing oxygen by the liquefaction and rectification of air, which comprises, passing strearns of oxygen and nitrogen products of rectification through separate paths in at least two heat exchange Zones connected in series, each of said Zones containing at least three paths in heat exchange relation with each other, passing a stream of air at about '70 to about 85 pounds gauge and at a temperature of about 70 to about 110 F. through a third path in the first Zone in heat exchange relation with the oxygen and nitrogen streams flowing through their respective paths in said rst zone, expanding a minor portion of the air leaving said first zone, thereby cooling said portion of the air, mixing the thus cooled air with the nitrogen. stream owing through said rst zo-ne, the amount of cold thus introduced into the process being adequate to compensate for cold losses resulting from the diierence in enthalpy between the :air introduced into and the products of rectification withdrawn from the process and for heat leaks into the system, passing the remainder of the air leaving said first zone through a third path in the second zone in heat exchange relation with the `oxygen and nitrogen streams flowing through their respective paths in said second zone, regulating the flow of air, nitrogen and oxygen into and from the second zone so that the temperature within said second zone is suchas to effect substantially complete removal of carbon dioxide from the air in its passage through its heat exchange path in said second zone and the difference between the temperature of the air and the weighted average temperature of the nitro gen and oxygen at the colder end of said second Zone falls withing the range of about 5 to about F., and periodically reversing the flow of air and nitrogen through their respective paths in said'zones, the air upon reversal flowing through the paths in the two zones through which had previously flowed the nitrogen and the nitrogen flowing through the paths through which had previously flowed the air, whereby upon each reversal the nitrogen substantially completely removes the carbon dioxide deposited in the second Zone during the preceding step oi the process.

3. A process for producing oxygen by the liquefa-ction and rectication of air, which comprises, passing streams of oxygen and nitrogen products of rectication through separate paths in at least two heat exchange Zones connected in series, each of said zones containing at least three paths in heat exchange relation with each other, passing a stream or air at about 70 toabout 85 pounds gauge and a temperature of about 70 to about F. through a third path in the iirst Zone in heat exchange relation with the oxygen and nitrogen streams flowing through their ren spective paths in said rst Zone, expanding a minor portion of the air leaving said iirst zone and mixing the expanded portion of the air with the nitrogen stream ilowing through said rst Zone, thereby cooling this nitrogen stream, the amount of cold thus introduced into the process being adequate to compensate for cold losses resulting from the dierence in enthalpy between the air introduced into and the products of rectiiication withdrawn from the process and. for heat leaks into the system, passing the remainder of the air leaving said rst zone through. a third path in the second zone in heat exchange relation with the oxygen and nitrogen streams flowing through their respective paths in said second zone, regulating the now of air, nitrogen and oxygen into and from the second zone, so thatthe` temperature within said second zone is such as to effect substantially complete removal of carbon dioxide from the air in its passage through its path in said second zone and the dierence between the temperature of the air and the Weighted average temperature of the nitrogen and oxygen at the colder end of said second zone is about 6 to about 8 F., and periodically reversing the iiow of air and nitrogen through their respective paths in said two Zones, the air upon reversal flowing through the paths in the two zones through which had previously flowed the nitrogen and the nitrogen flowing through the paths in the said two zones through which had previously flowed the air, whereby upon each re# versal the nitrogen substantially completely re moves the carbon dioxide deposited in the second zone during the preceding step of the process.

4. A process for producing oxygen by the liquefaction and rectication of air, which cornprises, passing an air stream at about 70 to 85 pounds gauge and a temperature of 70 to 110 F. through a path in a zone containing three paths in heat exchange relation with each other, passing streams of oxygen and nitrogen products of rectiiication respectively through the two other paths in said zone in heat exchange relation with the air stream, the air stream thus being cooled to a temperature suiilcient to substantially com pletely remove all moisture therefrom, expanding from about 5% to about 10% by volume of the air leaving said zone and imparting the cold thus produced to one of said streams flowing between the rst Zone and a second zone, the amount of cold thus introduced into the process being adequate to compensate for cold losses resulting from the difference in enthalpy between the air introduced into and the products of rectication Withdrawn from the process and for heat leaks 11Y into the system, cooling the remainder of the air leaving said first Zone by flowing it through a path in said`second zone containing three paths in heat exchange relation with each other, passing-streams of oxygenrand nitrogen products of rectification Y respectively through two other paths in said second Zone in` heat exchange relation with the air stream and thereby cooling the `air stream to a temperature sufncient to remove substantially all carbon dioxide therefrom, passing the thus cooled air stream fromY the second vzone to a rectification system in which the aforesaid streams ofoxygen and nitrogen produ-cts of rectification are formed, and periodically reversing the flow of airvand nitrogen streams through their respective paths in the said two Y zones, theV air stream upon reversal flowing throughY the paths in the two zones through which had previously owed the nitrogen stream and the'rnitrogen stream flowing through the paths in the said two' Zones through which had previously flowed the air stream, whereby upon each reversal the nitrogen stream substantially completely removes the carbondioxide deposited in the second-mentioned zone `and the frost deposited in theVrst-mentioned zone during the preceding step of the process.

- v5. A process for producing oxygen by the liquefaction and rectification of air, which comprises, passing air at about 70 to about 35 pounds gauge and a temperature of about '70 to about 110 F. through a path in a zone containing three ond zone divided into three paths, iiowing oxygen and nitrogen products of rectiiication respectively through the'other two paths in said second zone in heat exchange relation with the air thereby cooling the air to a temperature of about -260 to about 280 F., the difference between the temperature of the air and the weighted average temperature of the nitrogen and oxygenV at the colder end of said second zone being within the range of about 5 .to about 10 F., expanding about 7% by volume of the air leaving the first zone to a pressure of about 5 pounds and aV temperature of about 215 F., mixing the cold air thusrproduced with the nitrogen product of Vrectication passing through the rst Zone in heat exchange relation with the air and oxygen passing therethrough, and periodically reversing the iowV of air and nitrogen through their respective paths Y in the said twoV zones, the air upon reversal fiowing through the paths in the two Zones through which had previously iiowed the nitrogen and the nitrogen flowing through the paths in the 'said two zonesY through which had previously flowed the air, whereby upon each reversal the nitrogen substantially completely removes the carbon dioxide deposited in the second-mentioned'zone and the frost Vdeposited in the inst-mentioned zone during the preceding step in the process.

6. A process Vfor producing oxygen by the liquefaction and rectication of air,which ccmprises passing streams of oxygen and nitrogen products ofV rectification through at least two heat exchange zones connected in series, passing nitrogen and oxygen products of rectification passing through said first zone, expanding a minorportion of the air leaving said first zone and imparting the refrigeration thus produced to one of said oxygen and nitrogen streams passing through said rst Zone, passing the remainder o" the air through the second Zone to recover the cold content of the nitrogen and oxygen products of Yrectification passing through said second Zone, maintaining the temperature within said second.Y Zone such as to effect substantially complete removal of ycarbon dioxide from the air in its passage therethrough, maintaining the temperature diference between the temperature of the air and the weighted average temperature of the nitrogen and oxygen at the colder endV of said second Zone within Ythe range of from 5 to 10 F. and periodically reversing the flow of air and nitrogenV through their respective paths of iow in said second zone, the air upon reversal owing through the path through which had previously owed the nitrogen and the nitrogen flowing through Vthe path through which had previously owed the airfwhereby upon each reversal the nitrogen substantially completely re-V moves the carbon dioxide deposited in said second zone during the preceding step of the process.

'7. Alprocess for producing oxygen by the liquefaction and rectication of air; which comprises passing a stream of rectication product through Vtaining the temperature within at least one of said Zones such as to effect substantially complete removal of a condensible fconstituent'from the air inY its passage therethrough, maintaining the temperature'diierence between the temperature of the air leaving and the temperature ofthe rectication product entering the zone in which said substantially complete removal of a condensible constituent takes place such that it falls within the range of about 5 to 10 F., and periodically reversing the ow of air and rectification product through their respective paths in atY least the Zone where saidsubstantially complete removal of a condensible 'constituent takes place whereby upon each of said reversals the rectica- Y tion product substantially completely removes the Y ,Y condensible constituent deposited during the preceding step of the process. Y Y 1 Y V8. A process for producing oxygen by the liquefaction and rectification of air, which comprises, passing a stream of rectication product through a path in at least two heat exchange Zones connected in series, passing a stream of airthrough another path in the first heat exchange Zone Vin heat exchange relation with the rectification product passing therethrough, the air thus being cooled to a temperature effecting substantially complete'rernovalof moisture'rom saidvair, then expandingV a minor portion'of the air leaving said l rst zone and imparting the refrigeration thus a stream of air through the'rst of said heat exchange zones to Vrecover the *cold content of the produced to one of said streams flowing between said iirst zone and the second zone, passing the. remainder of. the air leaving said first zone through a path in said second Zone in heat exchange relation with the rectification product passing therethrough, regulating the flow of air and rectification product so that the temperature within said second zone is such as to effect substantially complete removal of a condensible constituent from the air in its passage therethrough and the temperature difference between the air leaving and the rectification product entering said second Zone falls within the range of about to about 10 F., and periodically reversing the How of air and rectication product through their respective paths in at least said second zone whereby upon each of said reversals the rectication product substantially completely removes the condensible constituent deposited during the preceding step of the process.

9. A process for producing oxygen by the liquefaction and rectification of air, which "comprises, passing a stream of rectification product through a path in at least two heat exchange zones connected in series, passing a stream of air at about 70 to about 85 pounds gauge through another path in the rst heat exchange Zone in heat eX- change relation with the rectication product passingtherethrough, the air thus being cooled to a temperature effecting substantially complete removal of moisture from said air, then expanding a minor portion of the air leaving said first zone and imparting the refrigeration thus produced to one of said streams owing between said rst zone and the second zone, passing the remainder of the air leaving said first zone through a path in said second zone in heat exchange relation with the rectication product passing therethrough, regulating the flow of air and rectication product so that the temperature within said second zone is such as to effect substantially complete removal of carbon dioxide from the air in its passage therethrough and the temperature difference between the air leaving and the rectification product entering said second Zone falls within the range of about 5 to about 10 F., and periodically reversing the flow of air and rectication product through their respective paths in said second zone whereby upon each of said reversals the rectication product substantially completely removes the carbon dioxide deposited during the preceding step of the process.

FRANK J. JENNY. EDWARD G. SCHEIBEL.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,626,345 Le Rouge Apr. 26, 1927 2,460,859 Trumpler Feb. 8, 1949 FOREIGN PATENTS Number Country Date 469,943 Great Britain Aug. 3, 1937 601,154 Germany July 19, 1934 

1. A PROCESS FOR PRODUCING OXYGEN BY THE LIQUEFACTION AND RECTIFICATION OF AIR, WHICH COMPRISES, PASSING STREAMS OF OXYGEN AND NITROGEN PRODUCTS OF RECTIFICATION THROUGH SEPARATE PATHS IN AT LEAST TWO HEAT EXCHANGE ZONES CONNECTED IN SERIES, EACH OF SAID ZONES CONTAINING AT LEAST THREE PATHS IN HEAT EXCHANGE RELATION WITH EACH OTHER, PASSING A STREAM OF AIR AT ABOUT 70 TO ABOUT 85 POUNDS GAUGE THROUGH A THIRD PATH IN THE FIRST ZONE IN HEAT EXCHANGE RELATION WITH THE OXYGEN AND NITROGEN STREAMS FLOWING THROUGH THEIR RESPECTIVE PATHS IN SAID FIRST ZONE, EXPANDING A MINOR PORTION OF THE AIR LEAVING SAID FIRST ZONE AND IMPARTING THE REFRIGERATION THUS PRODUCED TO AT LEAST ONE OF SAID OXYGEN AND NITROGEN STREAMS FLOWING THROUGH SAID FIRST ZONE, PASSING THE REMAINDER OF THE AIR THROUGH A THIRD PATH IN THE SECOND ZONE IN HEAT EXCHANGE RELATION WITH THE OXYGEN AND NITROGEN STREAMS FLOWING THROUGH THEIR RESPECTIVE PATHS IN SAID SECOND ZONE, REGULATING THE FLOW OF AIR, NITROGEN AND OXYGEN INTO AND FROM SAID SECOND ZONE SO THAT THE TEMPERATURE WITHIN SAID SECOND ZONE IN SUCH AS TO EFFECT SUBSTANTIALLY COMPLETE REMOVAL OF CARBON DIOXIDE FROM THE AIR IN ITS PASSAGE THROUGH ITS PATH IN SAID SECOND ZONE AND THE DIFFERENCE BETWEEN THE TEMPERATURE OF THE AIR AND THE WEIGHTED AVERAGE TEMPERATURE OF THE NITROGEN AND OXYGEN AT THE COLDER END OF SAID SECOND ZONE FALLS WITHIN THE RANGE OF ABOUT 5* TO ABOUT 10* F., AND PERIODICALLY REVERSING THE FLOW OF AIR AND NITROGEN THROUGH THEIR RESPECTIVE PATHS IN SAID ZONES, THE AIR UPON REVERSAL FLOWING THROUGH THE PATHS THROUGH WHICH HAD PREVIOUSLY FLOWED THE NITROGEN AND THE NITROGEN FLOWING THROUGH THE PATHS THROUGH WHICH HAD PREVIOUSLY FLOWED THE AIR, WHEREBY UPON EACH REVERSAL THE NITROGEN SUBSTANTIALLY COMPLETELY REMOVES THE CARBON DIOXIDE DEPOSITED IN SAID SECOND ZONE DURING THE PRECEDING STEP OF THE PROCESS. 